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  • Voltage

    I am getting 62 Volts from my panels but when I check the voltage at the charge controller I!m only reading 43 volts. Why the big voltage drop? Is this normal or do I have a problem somewhere? If anyone can answer appreciate it.

  • #2
    Originally posted by Slidegate View Post
    I am getting 62 Volts from my panels but when I check the voltage at the charge controller I!m only reading 43 volts. Why the big voltage drop? Is this normal or do I have a problem somewhere? If anyone can answer appreciate it.
    Is that 62 volts being measured with nothing connected to your panels? (ie open circuit voltage Voc). If not then I would say you have almost a voltage drop of 20vdc.

    What wire size are you using and how far apart are the points you measured 62v and 43v?

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    • #3
      Not enough info to answer your question. As SE alluded to are you measuring Open Circuit Voltage, or Closed Circuit Voltage.

      If you go to the panel, disconnect it, then measure the voltage, you are reading Open Circuit Voltage aka Voc which is what I suspect you are doing. Then when you measure at the controller you are measuring something close to Vmp where current is flowing. A panel with a Voc of 63 volts wil have a Vmp of roughly of 50 volts.

      The other possibility is you wire is way too long and to small of a gauge. When current flows through a wire, a voltage drop is developed due to the resistance of the wire. The voltage is the product of both current and resistance and mathematically expressed as Voltage = Current x Resistance. Wire resistance is determined by it length and size. In a properly designed system you should limit voltage drop to 2% or less. It does not happen by accident and requires the designer to account for it in the design stage.
      MSEE, PE

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      • #4
        Yes I am reading 62 open circuit voltage. Wire size from panel is #4 then go to #6 AWG for about 8 feet to the controller

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        • #5
          Originally posted by Slidegate View Post
          Yes I am reading 62 open circuit voltage. Wire size from panel is #4 then go to #6 AWG for about 8 feet to the controller
          The open circuit voltage reading will go down once you connect the panels to a charge controller. That is expected.

          A wire size of #6 for that short distance should not create any large voltage drop to be concerned of.

          Tomorrow measure the voltage at the charge controller around Noon. Also provide the spec of those pv panels, how many you have and how they are wired to the CC.

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          • #6
            Originally posted by Slidegate View Post
            Yes I am reading 62 open circuit voltage. Wire size from panel is #4 then go to #6 AWG for about 8 feet to the controller
            OK you are doing it incorrectly, well just do not understand what is going on. Solar panels are not Voltage Sources, they are Current Sources. Only thing Voc tells you is the panel is working OK with no load, nothing more.

            When you draw current from a solar panel the voltage is going to drop, and drop a lot. Can go all thee way down to ZERO volts if shorted out which is another test called ISC or current short circuit.

            What you want to know is when the panel is producing full rated power, is the voltage drop between the Panel output connector, and the Controller Input connector. You want it to be less than 2%. To do that you have to have either the battery deeply discharged, or enough load devices turned on that exceed the panel output at high noon on a very bright clear sunny day. Does no good what so ever at low power levels. Well it will if you have a problem.

            The issue is low voltage. All power wire is assumed to be used at much higher voltages of 240/120 up to 600 volts and higher. However power wire is rated by the amount of current it can safely handle. Most circuits in your house are 20 amps. and NEC says you must use at least a 12 AWG copper wire. That is just fine for 120 volts as you can have a 1-way distance 50 feet you loose 6 volts which is fine at 120 volts or a 5% loss in voltage and power. That would be a 120 volts x 20 amps = 2400 watts. But 20 amps on a 12 volt circuit is just 240 watts and a 50% voltage/power loss making it unusable. At 50 feet you would need a 1/0 AWG cable one the size of a big cigar that cost 11 times more than 12 AWG per foot.
            MSEE, PE

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            • #7
              The working voltage reading will be strongly affected by the type of charge controller... PWM or MPPT. The position of the sun in the sky doesn't matter much, and waiting until noon could complicate the interpretation if the controller has moved out of bulk and into absorb.

              With PWM in the bulk stage (100% duty), the panel voltage will be the same as the battery voltage, plus any voltage rise from the transmission and from the controller itself, and you will see it rise over time if you take a series of measurements starting when the sun comes up in the morning. With MPPT in the bulk stage, you should see the panel voltage drop as the sun gets higher, since the array will warm up and the Vmp will drop with increasing temperature.
              CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

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